The purpose of this grant is to develop techniques for use in the ?early? detection of keratoconus (KC) and identify genetic variants that contribute to its development. KC is a complex genetic eye disorder and a leading cause of corneal transplantation in the young, with approximately 300,000 affected individuals in the US. Undiagnosed, subclinical KC is one of the major causes for complications of LASIK (Laser-in-situ- Keratomilieusis) surgery, commonly performed for vision correction. In the past two decades we have made major improvements to the early diagnosis of KC and have also made significant contributions to the delineation of major genetic determinants of KC through genome wide linkage studies (GWLS), fine mapping, and genome wide association studies (GWAS). In this proposal, we intend to follow up on these studies using new powerful approaches to achieve the following specific aims: In Aim 1 we will combine corneal optical coherence tomography (OCT) and Pentacam HR Scheimpflug Tomography (PST), new technologies that measure both the anterior and posterior surface of the cornea, with videokeratography (VK), a method which revolutionized KC diagnosis, to characterize criteria and to improve the diagnosis of subclinical KC. In Aim 2, to identify additional KC genes, we will perform a 2.5 million SNP GWAS, with an additional 6,000 SNPs, to finemap already identified genes. We will confirm these results in a separate cohort of KC patients. For this twostage GWAS design we are assembling the largest group of KC patients described to date: 2000 KC patients in total, 1,000 for the GWAS discovery stage and 1,000 for the confirmation stage. The controls for GWAS discovery will come from the Cardiovascular Health Study (CHS; 3300) and for confirmation will come from 400 subjects with VK, PST, and OCT measurements under Aim 1 and 600 ?convenience controls? f rom the Cholesterol and Pharmacogenetics (CAP) study. In our current state of knowledge, the most cost-effective approach to increase the number of identified KC genes is to proceed with the expanded GWAS proposed herein. In Aim 3, we will test the impact of the genes identified in Aim 2 on the ?early? subclinical phenotypes identified through the use of VK, PST and OCT measures in Aim 1. Lastly, for the second part of Aim 3, we will investigate the potential function of KC variants by testing their ability to influence gene structure, expression and function in corneal cell models, including iPS cells derived from corneal keratocytes developed by our research team. The results of these studies will help advance our understanding of the genetic susceptibility to KC and may result in novel treatment options to slow the progression of the disease.